A model for estimating advisory speeds for horizontal curves in two-lane rural roads

Horizontal curves are designed using a design speed, which is the speed used to determine the geometric features of highways. In sharp curves, drivers sometimes exceed the design speed. Depending of the difference between design speed and operating speed, drivers can face risky situations, which can be mitigated using signs informing drivers of advisory speeds. Advisory speeds at the horizontal curves are normally estimated as a function of the lateral acceleration for a maximum driving speed, at which comfort is low. This paper proposes an analytical model to estimate advisory speeds based on ball-bank readings and consistency concepts. Field data were obtained using a digital ball-bank indicator, an accelerometer, and a GPS logger. Readings were obtained on 24 test sections at speeds between 40 and 110 km/h. The model proposed yields an advisory speed value and a limit ball-bank angle that require consistent behavior of drivers.